Three-page explanation of Dasher

Imagine a library containing all possible books,
ordered alphabetically on a single shelf.
Books in which the first letter is "a" are
at the left hand side.
Books in which the first letter is "z" are at the right.
In picture (i) below,
the shelf is shown vertically with "left" (a) at the top
and "right" (z) at the bottom.
The first book in the "a" section
reads "aaaaaaaaaaaa..."; somewhere to its right are
books that start "all good things
must come to an end...";
a tiny bit further to the right are books that
start "all good things must come to an enema...".

(i)

(ii)

(iii)

When someone writes a piece of text, their choice
of the text string can be viewed as a choice of a book
from this library of all books - the book that contains exactly the
chosen text.
How do they choose that book? Let's imagine they want
to write "all good things..."

First, they walk into the "a" section of the library.
There, they are confronted by books starting "aa", "ab", "ac,.... "az"
[Picture (ii)].
Looking more closely at the "al" section, they can find books
starting "ala", "alb",... "alz"
[Picture (iii)].

By looking ever more closely at the shelf, the writer
can find the book containing the text he wishes to write.
Thus writing can be described as zooming in on
an alphabetical library, steering as you go.